1. Field of the Invention
The present invention relates, in general, to a blower that is referred to as a sirocco fan and, more particularly, to a blower, which is capable of increasing its blowing efficiency while reducing its noise, in such a way that the expansion angle of its scroll housing is increased in a discharge region and discharge guides are mounted to the discharge opening of the scroll housing for reducing the flow resistance of air.
2. Description of the Prior Art
Generally, a sirocco fan is a blower that is widely employed in household electronic appliances. An example of such a sirocco fan that is applied to a combined electronic range and hood is illustrated in FIG. 1.
The combined electronic range and hood shown in FIG. 1 comprises a case 1, a cavity 5 provided in the case 1 for positioning food for cooking, a magnetron 3 for radiating electronic waves to the interior of the cavity 5, a fan 4 for cooling the magnetron 3, a pair of blowers 10 positioned over the cavity 5 for discharging smoke, which is generated in a gas range (not shown) disposed beneath the case 1, to the outside by means of a drive motor 2, and a discharge passage formed in the side portions of the case 1 for allowing the smoke generated in the gas range to be moved. The smoke that is sucked from an inlet positioned on the bottom of the case 1 rises through the discharge passage, flows through the blowers 10, and is discharged to the outside through a connecting duct 21.
As illustrated in FIG. 2, each of the blowers 10 comprises an impeller 11 for sucking air and a scroll housing 12 for guiding and discharging the air sucked by the impeller 11 to a discharge opening 12b. 
The impeller 11 comprises a plurality of blades 11a retained by means of a rib 11b and is connected to the drive motor. The scroll housing 12 is designed in such a way that air is sucked through an inlet 12a while being guided by a bell mouth 13, and discharged through a discharge opening 12b while flowing through a passage that is gradually enlarged from a cutoff position C. In other words, when the impeller 11 connected to the drive motor is rotated, air in front of the inlet 12a is sucked, moved to the discharge opening 12b along the gradually expanded passage of the scroll housing 12, and is discharged to the outside. Therefore, since noise and air flow rate generated in the blower 10 are varied sensitively in accordance with the design of the scroll housing 12, attempts have been made to reduce the noise and increase the air flow rate.
In FIGS. 2 and 3, reference characters xcex80, xcex8c, and xcex8x respectively denote a reference angle, a cutoff start angle measured counterclockwise from the reference angle xcex80 to a cutoff start position and an optional angle measured counterclockwise from the reference angle xcex80 to an optional position.
FIG. 3 is a front view showing the scroll housing of the conventional blower that is designed using an Archimedic curve and an exponential curve. FIG. 4 is a graph wherein expansion angles are plotted for a case where the scroll housing of the conventional blower is designed using the Archimedic curve and the exponential curve.
As shown in FIGS. 3 and 4, such a conventional scroll housing may be classified into one type that is designed using the Archimedic curve or another type that is designed using an exponential curve.
In a method of constructing the contour of the scroll housing 12 using the Archimedic curve, its curvature radius is increased proportionally according to a mean velocity theory when the contour of the scroll housing 12 has been determined. When an expansion angle is xcex1, the curvature radius Rx of the scroll housing at a position, where an angle measured from the reference angle xcex80 is xcex8x, is calculated by the following equation 1.
Rx=Roxc3x97(1+xcex8xxc3x97xcfx80/180xc3x97tan xcex1)xe2x80x83xe2x80x83Equation 1
wherein Ro denotes the radius of the impeller.
In a scroll housing 20 constructed using an exponential curve in which its curvature radius is increased exponentially, the curvature radius Rx of the scroll housing is calculated by the following equation 2 when an expansion angle is xcex1e and an angle measured from the reference angle xcex80 is xcex8x.
Rx=Roxc3x97exp(tan xcex1exc3x97xcex8xxc3x9790 /180)xe2x80x83xe2x80x83Equation 2
However, in the conventional blower, since the sum of a curvature radius R180 when the angle xcex8x=180xc2x0 and a curvature radius R360 when the angle xcex8x=360xc2x0 is the width of the scroll housing in a case where the Archimedic curve is used and the width of the scroll housing is fixed, the expansion angle xcex1 is fixed when the radius Ro of the impeller is determined. For example, when the radius Ro of the impeller is 40 mm and the width of the scroll housing is restricted to 105 mm, the expansion angle in the Archimedic curve is 3.799xc2x0. Therefore, since the expansion angle, which influences the air flow rate, is fixed if the radius of the impeller and the width of the scroll housing are fixed, the radius of the impeller should be reduced so as to increase the expansion angle. However, this causes problems wherein flowing performance is reduced and noise is increased.
Additionally, when the widths of the scroll housing are the same, the scroll housing that is constructed using the exponential curve has a small curvature radius in comparison with the scroll housing that is constructed using the Archimedic curve.
On the other hand, in order to improve the discharge performance by increasing the air flow rate of the combined electronic range and hood shown in FIG. 1, the width W and the entire length Lv of the blower 10 shown in FIG. 5 should be increased.
In order to increase the width W of the blower 10, inner cooking space, or the cavity 5 should be reduced in a same-sized combined electronic range and hood. In order to increase the entire length of the blower 10, the length Lh of the discharge opening 12b should be increased. In such a case, the air flow rate can be increased while flow loss and generation of noise are minimized.
However, since the width Ld of the connecting duct 21 is restricted to a certain standard size in the combined electronic range and hood that is generally used in kitchens and shown in FIG. 1, the length Lh of the discharge opening of the scroll housing in communication with the connecting duct 21 should be restricted even though the entire length Lv of the blower 10 shown in FIG. 5 is designed to be greater.
As a result, if the length Lv of the blower 10 is increased under a condition that the size of the discharge opening 12b of the scroll housing 12 is restricted, the flow loss is increased in the side space Z of the discharge opening 12b and the scroll housing 12. Consequently, the air flow rate is scarcely increased and the collision of flow is increased, so that severe noise is generated.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a blower, in which its expansion angle is reduced in a region of air suction and its expansion angle is increased in a region of air discharge, thereby improving flowing performance and reducing noise.
Another object of the present invention is to provide a blower, which is capable of reducing flow loss that is generated when air is discharged by forming a discharge guide in a scroll housing, thereby improving the discharge performance of air.
In order to accomplish the above object, the present invention provides a blower, comprising an impeller provided with a plurality of blades and a scroll housing for guiding and discharging air sucked by the impeller to the outside, the scroll housing surrounding the impeller, wherein the expansion angle of the curvature radius of the contour of the scroll housing is to be less than an expansion angle in conformity with an Archimedic curve in a suction region ranging from a cutoff start angle to 160-200xc2x0 from a reference angle and to be greater than the expansion angle in conformity with the Archimedic curve in a discharge region ranging exceeding 160-200xc2x0 from the reference angle.
In addition, the present invention provides a blower, comprising a scroll housing, an impeller, and guide means mounted to a discharge opening of said scroll housing.